Silicon of ultra-high purity is used extensively in the electronics and photovoltaic industries. High purity granular polysilicon materials with only trace of amounts of contamination measured at the part per billion levels are often required. Producing such materials is possible, but then extreme care must be taken in any handling, packaging or transportation operations to avoid subsequent contamination.
Conventional feeding technology used to convey granular polysilicon materials includes components having metal in their construction (e.g., valves, conduits, etc.). When protective coatings or linings are compromised, or when wear occurs at the interfaces of moving parts, for example, contamination of metal parts can occur, which is unacceptable.
In addition, conventional feeders may not provide sufficient control over the rate of flow granular polysilicon and/or the flow rate range. Conventional vibrating tray feeders may achieve a feed rate range between a lowest controllable feed rate and a highest controllable feed rate of only about 1:50, but a much higher feed rate range is desirable. Other conventional approaches allow higher feed rate ranges to be achieved, but only with apparatus having multiple parts within the control volume of the flowing material that must move relative to each other, such as auger screws, rotary vanes and other similar structures. Multiple parts in relative motion within the control volume, however, leads to a greater risk of contamination.
Also, such conventional feeders are difficult to purge with a suitable process gas and/or clean in part because of their complicated constructions. The multi-piece constructions typically require an extensive use of seals to prevent leakage through components that move relative to each other.
Conventional vibratory solids conveyors typically have a rigid container constrained by linkages and/or springs that can be driven by an eccentric weight assembly coupled to an electric motor or an electromagnetic drive in a desired motion, such as elliptical rotation that includes horizontal and vertical components.
Conventional approaches to conveying solids, including vibratory conveyors, screw augers, belt conveyors and other similar devices, are not capable of achieving high performance over a large range of flows while ensuring that ultrahigh purity is maintained.